Function Of Electronic Stopping Power Research Articles

Measurement of the quenching and channeling effects in a CsI crystal used for a WIMP search

We have studied channeling effects in a cesium iodide (CsI) crystal that is similar in composition to the ones being used in a search for Weakly Interacting Massive Particles (WIMPs) dark matter candidates, and measured its energy-dependent quenching factor, the relative scintillation yield for electron and nuclear recoils. The experimental results are reproduced with a GEANT4 simulation that includes a model of the scintillation efficiency as a function of electronic stopping power. We present the measured and simulated quenching factors and the estimated effects of channeling.

Swift heavy ion irradiation of water ice from MeV to GeV energies

Context. Cosmic ray ion irradiation affects the chemical composition of and triggers physical changes in interstellar ice mantles in space. One of the primary structural changes induced is the loss of porosity, and the mantles evolve toward a more compact amorphous state. Previously, ice compaction was monitored at low to moderate ion energies. The existence of a compaction threshold in stopping power has been suggested.Aims. In this article we experimentally study the effect of heavy ion irradiation at energies closer to true cosmic rays. This minimises extrapolation and allows a regime where electronic interaction always dominates to be explored, providing the ice compaction cross section over a wide range of electronic stopping power.Methods. High-energy ion irradiations provided by the GANIL accelerator, from the MeV up to the GeV range, are combined with in-situ infrared spectroscopy monitoring of ice mantles. We follow the IR spectral evolution of the ice as a function of increasing fluence (induced compaction of the initial microporous amorphous ice into a more compact amorphous phase). We use the number of OH dangling bonds of the water molecule, i.e. pending OH bonds not engaged in a hydrogen bond in the initially porous ice structure as a probe of the phase transition. These high-energy experiments are combined with lower energy experiments using light ions (H, He) from other facilities in Catania, Italy, and Washington, USA.Results. We evaluated the cross section for the disappearance of OH dangling bonds as a function of electronic stopping power. A cross-section law in a large energy range that includes data from different ice deposition setups is established. The relevant phase structuring time scale for the ice network is compared to interstellar chemical time scales using an astrophysical model.Conclusions. The presence of a threshold in compaction at low stopping power suggested in some previous works seems not to be confirmed for the high-energy cosmic rays encountered in interstellar space. Ice mantle porosity or pending bonds monitored by the OH dangling bonds is removed efficiently by cosmic rays. As a consequence, this considerably reduces the specific surface area available for surface chemical reactions.

Production and stability of radiation-induced defects in MgAl2O4 under electronic excitation

This paper investigates the formation process of radiation-induced defects in magnesium aluminate spinel and their stability using transmission electron microscopy, with emphasis on the effects of electronic excitation. Small interstitial-type dislocation loops disappeared under electron-induced electronic excitation. The elimination rate of the loops was found to be one order higher than for α-alumina. The disappearance of dislocation loops by a dissociation mechanism into isolated interstitials is discussed through analysis of the growth-and-shrink process of the loops. HARECXS analysis on cross section specimens irradiated with 350MeV Au ions has shown the progress of cation disordering along ion tracks to be a function of electronic stopping power, (dE/dx)e. Cations were found to exchange their sites toward a random configuration. Such disordering appears from (dE/dx)e=10keV/nm, and increases in size with increasing (dE/dx)e to reach nearly 10nm in diameter at 30keV/nm, under an assumption of a fully disordered configuration.

Ion-beam damage and non-radiative exciton decay in LiNbO 3

A model to account for the defects generated by ion irradiation in the electronic loss regime, and based on non-radiative decay of self-trapped excitons, is discussed and compared to experiments. It takes into account the competing role of the light-emission (radiative) and defect-creation (non-radiative) decay channels. Calculations are applied to LiNbO 3, a useful electro-optic crystal, where a large number of relevant experimental data are available. The model explains the strong nonlinear dependence of the defect creation rates as a function of electronic stopping power ( thresholding behavior). It also satisfactorily accounts for the formation and growth of amorphous layers by ion-beam irradiation at moderate fluences, φ>10 13 cm −2. Moreover, it also provides the right trend and reasonable quantitative accordance to data showing the dependence of the track radius on stopping power in single-impact experiments. Finally, the model determines the light emission yield during irradiation. In particular, it predicts that the number of photons emitted by ion impact first increases and then decreases monotonically with increasing electronic stopping power.

A fast screening technique to evaluate detector response

A fast screening technique to evaluate detector response was demonstrated using a silicon detector. Pulse height was measured for H, He, Be, C, O, Mg, Si, Ni, Zr and Au ions over a wide energy range using a time-of-flight (TOF) telescope. Using a scattering or recoil process, a secondary beam with a continuous energy distribution but low intensity is generated to avoid direct beam exposure of the Si detector. Prior to impinging on the Si detector, the energy of individual ions is determined from the TOF and its tabulated isotopic mass. The pulse height–energy calibration for ions with a given atomic number can be described by a linear relationship with small systematic deviations. For particles that have the same velocity (∼500 keV/nucleon), a non-linear dependence on efficiency of electron–hole pair collection is observed as a function of electronic stopping power. The detector response is studied using He ions, and the measured energy resolution is given as function of deposition energies over a wide energy range.